Although the progress of the fight against the COVID-19 in the U.S. remains, in the words of science writer Ed Yong, a "patchwork pandemic," the numbers of new cases of and deaths from the virus have either stabilized or are heading downward in most states and in the Washington, DC area, while hospital and public health contact tracing capacity has been growing. Practically every state has started cautiously easing restrictions on movement and public places and allowing shuttered businesses to reopen with social distancing measures in place. Although some politicians would like to declare victory over the virus, this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.
After I deployed this Twitter survey, some colleagues in medicine and public health suggested that I had left off some important terms, notably "social distancing," "exponential growth," and "flatten the curve." I agree. Notably, though, all four options received votes, and the top vote-getter, herd immunity, did not quite receive a majority. So I thought I'd provide my perspective, as a family physician and population health teacher, on what each of these terms mean and how they have sometimes been misinterpreted by the general public.What has been the most misused / misunderstood public health term during this pandemic?— Kenny Lin, MD, MPH (@kennylinafp) May 18, 2020
Herd immunity: the concept that once a pathogen has infected a certain percentage of the population (how much depends on how contagious it is) and they have developed immunity, there are fewer susceptible hosts, which not only slows the spread but also indirectly protects non-immune persons. For vaccine-preventable infections like measles and pertussis (which causes whooping cough), herd immunity is especially important for protecting persons who have contraindications to immunization (for example, infants too young to be vaccinated or immune-compromised persons).
However, for COVID-19, some have suggested that rapidly achieving herd immunity should be a national goal, even in the absence of an effective vaccine. They pointed at Sweden, an country that stands alone among developed nations in not instituting an economic lockdown (though mass gatherings have been banned and social distancing is still strongly encouraged). Nonetheless, by early May, only about 25 percent of the population of Stockholm had developed antibodies to SARS-CoV-2 and Sweden currently has the highest per-capita COVID-19 death rate in the world without any perceptible economic benefits. In New York City, in March and April the epicenter of the pandemic in the U.S., a study found that only 1 in 5 people had antibodies to the virus - far short of a herd immunity threshold even though hospitals and morgues were overrun and 1 out of every 400 people died. As Five Thirty Eight calculated, "If the [COVID-19] fatality rate is around 0.5 percent and 70 percent of Americans have to get sick before their immunity starts protecting others, that means more than 1.1 million people would die." Personally, I think that the most likely projection of 140,000 U.S. deaths given existing social distancing measures is a national catastrophe, but 1,100,000 deaths is totally unacceptable.
Quarantine: refers to the isolation of persons who have been exposed to a contagious disease for the maximum duration of the time it takes from the time of exposure to becoming symptomatic. For COVID-19, the recommended duration is 14 days. This is not the same thing as "self-isolation" of persons with known infections or "lockdown" (government-mandated travel restrictions). Yes, I intentionally misused this term in my previous post, but "self-isolation / lockdown reading" just sounded too weird.
Contact tracing: refers to the practice of identifying and contacting persons who have been exposed to a known infected individual so that they can be assisted in quarantining themselves and connected to resources (including health care) if needed. Smartphone tracking apps can help facilitate this process, but are not a substitute for real people working the phones. If you are interested in learning more about becoming contact tracers for your states and communities, Johns Hopkins University is offering an excellent free online course on this topic. For contact tracing to be effective in preventing new COVID-19 outbreaks, however, it is critical that the general population trusts the tracers and adheres to their recommendations. In a widely suspicious community, riled up by armed protests about government encroachment on their freedoms (to travel to one's second home, to work out at the gym, to go bowling, etc.), I worry that many people may ignore public health workers telling them to stay home, and will continue infecting others.
Antibody testing: blood testing for antibodies to SARS-CoV-2 that can help determine if an individual has been exposed to the virus. My colleague Dr. Mark Ebell has pointed out that with current far-from-perfect tests and a low prevalence in most communities (particularly in persons without respiratory symptoms), false positive test results will be common. Most critically, even a "true positive" antibody test result does not guarantee that an individual is protected from COVID-19, or for how long. We just don't know yet how durable immunity is or how long it lasts. So if you get a blood test that suggests you have antibodies, don't discard your mask or stop social distancing because you think you can't get infected or infect others.